use bincode;
use serde::{de::DeserializeOwned, Serialize};
//use std::collections::VecDeque;
use crate::types::{Mid, Sid};
use std::sync::Arc;

//Todo: Evaluate switching to VecDeque for quickly adding and removing data
// from front, back.
// - It would prob requiere custom bincode code but thats possible.
/// Support struct used for optimising sending the same Message to multiple
/// [`Stream`]
///
/// For an example usage see: [`send_raw`]
///
/// [`Stream`]: crate::api::Stream
/// [`send_raw`]: crate::api::Stream::send_raw
pub struct MessageBuffer {
    pub data: Vec<u8>,
}

#[derive(Debug)]
pub(crate) struct OutgoingMessage {
    pub buffer: Arc<MessageBuffer>,
    pub cursor: u64,
    pub mid: Mid,
    pub sid: Sid,
}

#[derive(Debug)]
pub(crate) struct IncomingMessage {
    pub buffer: MessageBuffer,
    pub length: u64,
    pub mid: Mid,
    pub sid: Sid,
}

pub(crate) fn serialize<M: Serialize>(message: &M) -> MessageBuffer {
    //this will never fail: https://docs.rs/bincode/0.8.0/bincode/fn.serialize.html
    let writer = bincode::serialize(message).unwrap();
    MessageBuffer { data: writer }
}

pub(crate) fn deserialize<M: DeserializeOwned>(buffer: MessageBuffer) -> M {
    let span = buffer.data;
    //this might fail if you choose the wrong type for M. in that case probably X
    // got transfered while you assume Y. probably this means your application
    // logic is wrong. E.g. You expect a String, but just get a u8.
    let decoded: M = bincode::deserialize(span.as_slice()).expect(
        "deserialisation failed, this is probably due to a programming error on YOUR side, \
         probably the type send by remote isn't what you are expecting. change the type of `M`",
    );
    decoded
}

impl std::fmt::Debug for MessageBuffer {
    #[inline]
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        //TODO: small messages!
        let len = self.data.len();
        if len > 20 {
            write!(
                f,
                "MessageBuffer(len: {}, {}, {}, {}, {:?}..{:?})",
                len,
                u32::from_le_bytes([self.data[0], self.data[1], self.data[2], self.data[3]]),
                u32::from_le_bytes([self.data[4], self.data[5], self.data[6], self.data[7]]),
                u32::from_le_bytes([self.data[8], self.data[9], self.data[10], self.data[11]]),
                &self.data[13..16],
                &self.data[len - 8..len]
            )
        } else {
            write!(f, "MessageBuffer(len: {}, {:?})", len, &self.data[..])
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::message::*;

    #[test]
    fn serialize_test() {
        let msg = "abc";
        let mb = serialize(&msg);
        assert_eq!(mb.data.len(), 11);
        assert_eq!(mb.data[0], 3);
        assert_eq!(mb.data[1], 0);
        assert_eq!(mb.data[7], 0);
        assert_eq!(mb.data[8], 'a' as u8);
        assert_eq!(mb.data[8], 97);
        assert_eq!(mb.data[9], 'b' as u8);
        assert_eq!(mb.data[10], 'c' as u8);
    }
}